I get full Windows resolution up to 5120x2880. Here are my settings:
iMac Display Resolution is set to: Default for display
Fusion Compatibility Setting: Use Hardware Version: 14
Fusion Display settings are:
- Accelerate 3D Graphics: ON, with 2048 MB Shared graphics memory
- Use full resolution for Retina display:
- Scaled high resolution: All View Modes
- Automatically adjust user interface in VM: ON
- VM Resolution:
- Single Window: Use Fusion Display Prefs
- Full Scree: Use Fusion Display Prefs
- I don't use Unity mode, so I don't know what the resolution is for it
In Windows 10:
- in Display settings:
- Fusion seems to turn Custom Scaling ON by default
- turn Custom Scaling OFF, you will be asked to log off/on
- Fusion resets Custom Scaling back to ON and sets mine to 450%
- with scale & layout changes at 450% I can easily read the text
- in full screen mode, resolution changes to: 5120x2880
Hope it works for you. Mine looks very sharp.
Brent